[1] Department of Radiology, Karolinska University Hospital, Stockholm,SE-171 76, Sweden
[2] Department of Medical and Health Sciences, Linköping University, Linköping,SE-581 83, Sweden
[3] FLOW & BioMEx, Department of Engineering Mechanics, Royal Institute of Technology KTH, Osquars Backe 18, Stockholm,SE-100 44, Sweden